Steam turbines and gas turbines are normally provided with a seal device capable of restricting a flow of a fluid in clearance between a stationary member and a rotational member, that is, for instance, clearance between rotor blades and members surrounding rotor blades or clearance between stationary vanes and a rotor.
For instance, JP5518022B discloses a seal device of a steam turbine provided with a step portion disposed on a tip portion of a blade and a seal fin disposed on a structural body. The step portion has at least one step surface facing the upstream side and protrudes toward the structural body. The seal fin extends toward the step portion and forms minute clearance between the seal fin and the step portion.
With the above seal device of a steam turbine, a separation vortex and a main vortex are formed on the upstream side of the seal fin, and the flow contraction effect of the separation vortex reduces leakage of steam that flows through the minute clearance.